Laser direct structuring (LDS) is a well know method in the art of producing electric and electronic devices. Especially for the aim of miniaturization, LDS enables size reduction of the device, whilst simultaneously equipping them with greater functionality, e.g. a higher density of circuits. Examples for such electronic devices are injection-molded circuit carriers, also known as molded interconnected devices (MID). MIDs are designed to be three dimensional (3D-MIDs). One intention of such 3D-MIDs is to combine the electrical and the mechanical functionalities in a single component. The circuit paths in such devices are integrated into the housing, thereby replacing conventional circuit boards. The weight and package size of such devices is significantly reduced in comparison to classic electronic devices and the integration of further functionalities, like e.g. the integration of sensors or antennas, is simplified. MID technology offers a greater freedom of design and due to a shortened process chain a significant potential of rationalization. With the method of laser structuring of MIDs it is possible to produce high-resolution circuit layouts also on complex three-dimensional carrier structures, thus integrating casings and circuit boards that previously were separated units in one device.
Main application fields of the MID technology are automotive electronics and telecommunication. However, also in the area of computer technology, household applications, as well as medical devices the benefit of the MID-technology is exploited.
Among the various technologies to produce such MIDs, additive or subtractive laser structuring is well known.
In US 2004/0241422, a method for laser structuring of circuit paths is disclosed. In this method circuit path structures are generated on an electrically non-conductive carrier material, where these paths consisting of metal seeds and a metallization subsequently applied to these seeds. The metal seeds resulted from the raising of electrically non-conductive metal compounds that are contained in a very finely divided form in a carrier material, by electromagnetic radiation. In doing so, the electrically non-conductive metal compounds are formed of thermally very stable inorganic metal compounds that are insoluble and stable in aqueous acidic or alkaline metallization baths and that remain unaltered in regions not irradiated by the laser. The process is based on doted thermoplastic materials on which tracks that are to be realized as circuits paths are activated by means of a focused laser beam. Said activated tracks are subsequently metalized in plating bathes, like e.g. electroless copper plating bathes.
Today, different carrier materials already doped with a metal-organic complex compounded that releases the needed metal seed when laser activated are available. Examples of such carrier materials are polycarbonates, polycarbonate acrylonitrile butadiene styrene blends, polyamides, poly urethane resins, liquid crystal polymers, polybutylene terephthalates, polyethylene terephthalates, and co-polymers of these.
EP1584708 A2 discloses a method for treating plastic substrates structured by means of a laser or generation of seed structures on the surface that are suitable for subsequent metallization. The substrates, after the laser structuring, are brought into contact with a process solution that is suitable for removal of the unintentional deposits that arise during the laser structuring. The treatment of the laser-structured substrates with a mixture of wetting agents and compositions that support the cleaning before metallization leads to sufficient removal of the unintentionally deposited metal seeds, without having a lasting damaging effect on the planned structured surface paths.
US 2007/0163887 A1 discloses a method of manufacturing a circuit carrier and the use of said method are proposed, said method comprising, after providing a printed circuit board (a), coating the circuit board on at least one side thereof with a dielectric (b), structuring the dielectric for producing trenches and vias therein using laser ablation (c) are performed. Next, a primer layer is deposited onto the dielectric, either onto the entire surface thereof or into the produced trenches and vias only (d). A metal layer is deposited onto the primer layer, with the trenches and vias being completely filled with metal for forming conductor structures therein (e). Finally, the excess metal and the primer layer are removed until the dielectric is exposed if the primer layer was deposited onto the entire surface thereof, with the conductor structures remaining intact (f).
Catalyst filled plastics for LDS can be copper-plated in the laser-activated areas using electroless copper plating solutions. In fact, the initiation of the copper growth on the laser structures substrate areas is slow in comparison to palladium activated copper plating on plastic substrates. This is especially true for plastics like ABS or ABS/PC blends, which are widely used e.g. for mobile phone antennas. Long deposition times and/or non sufficient coverage of activated areas are observed. To overcome this drawback, in today's processes often a two-step plating concept is used. In a first step a highly active, but unstable plating electrolyte solution is used, which provides a quick coverage (flash copper). Subsequently, a more stable electrolyte solution is used which only works if there is already copper deposited on the surface to be plated. This two-step concept is time and cost intensive.